Toward understanding of quark gluon plasma in relativistic heavy ion collisions
This presentation is the property of its rightful owner.
Sponsored Links
1 / 51

Toward understanding of Quark-Gluon Plasma in relativistic heavy ion collisions PowerPoint PPT Presentation


  • 100 Views
  • Uploaded on
  • Presentation posted in: General

Toward understanding of Quark-Gluon Plasma in relativistic heavy ion collisions. Tetsufumi Hirano Dept. of Physics The University of Tokyo. Introduction Basic Checks Energy density Chemical and kinetic equilibrium Dynamics of Heavy Ion Collisions Elliptic flow Jet quenching

Download Presentation

Toward understanding of Quark-Gluon Plasma in relativistic heavy ion collisions

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Toward understanding of quark gluon plasma in relativistic heavy ion collisions

Toward understanding of Quark-Gluon Plasma in relativistic heavy ion collisions

Tetsufumi Hirano

Dept. of Physics

The University of Tokyo


Outline

Introduction

Basic Checks

Energy density

Chemical and kinetic equilibrium

Dynamics of Heavy Ion Collisions

Elliptic flow

Jet quenching

Summary and Outlook

Discussion

OUTLINE


Physics of the qgp

Physics of the QGP

  • Matter governed by QCD, not QED

  • Frontier of high energy density/temperature

    Toward an ultimate matter (Maximum energy density/temperature)

  • Understanding the origin of matter which evolves with our universe

  • Reproduction of QGP in H.I.C.

    Reproduction of “early universe” on the Earth


History of the universe history of matter

History of the Universe ~ History of Matter

Quark Gluon Plasma

Hadronization

Nucleosynthesis

QGP study

Understanding

early universe


Little bang

Little Bang!

front

view

Relativistic Heavy Ion Collider(2000-)

RHIC as a time machine!

STAR

side

view

STAR

Collision energy

Multiple production

(N~5000)

Heat

100 GeV per nucleon

Au(197×100)+Au(197×100)


Basic checks

BASIC CHECKS


Basic checks i energy density

Basic Checks (I): Energy Density

Bjorken(’83)

Bjorken energy density

total energy

(observables)

t: proper time

y: rapidity

R: effective transverse radius

mT: transverse mass


Critical energy density from lattice

Critical Energy Density from Lattice

Stolen from Karsch(PANIC05);

Note that recent results seem to be Tc~190MeV


Centrality dependence of energy density

Centrality Dependence of Energy Density

Well above

ec from lattice

in central

collision at RHIC,

if assuming

t=1fm/c.

ec from lattice

PHENIX(’05)


Caveats i

CAVEATS (I)

  • Just a necessary condition in the sense that temperature (or pressure) is not measured.

  • How to estimate tau?

  • If the system is thermalized, the actual energy density is larger due to pdV work.

  • Boost invariant?

  • Averaged over transverse area. Effect of thickness? How to estimate area?

Gyulassy, Matsui(’84) Ruuskanen(’84)


Basic checks ii chemical eq

Basic Checks (II): Chemical Eq.

direct

Resonance decay

Two fitting parameters: Tch, mB


Amazing fit

Amazing fit!

T=177MeV, mB = 29 MeV

Close to Tc from lattice


Caveats ii

CAVEATS (II)

  • Even e+e- or pp data can be fitted well!

    See, e.g., Becattini&Heinz(’97)

  • What is the meaning of fitting parameters? See, e.g., Rischke(’02),Koch(’03)

  • Why so close to Tc?

    • No chemical eq. in hadron phase!?

    • Essentially dynamical problem!

Expansion rate  Scattering rate

(Process dependent)

see, e.g., U.Heinz, nucl-th/0407067


Basic checks iii radial flow

Basic Checks (III): Radial Flow

Blast wave model (thermal+boost)

Driving force of flow

pressure gradient

Inside: high pressure

Outside: vacuum (p=0)

Sollfrank et al.(’93)

Spectrum for heavier particles

is a good place to see radial flow.


Spectral change is seen in aa

Spectral change is seen in AA!

Power law in pp & dAu

Convex to Power law

in Au+Au

  • “Consistent” with thermal + boost picture

  • Large pressure could be built up in AA collisions

O.Barannikova, talk at QM05


Caveats iii

CAVEATS (III)

  • Not necessary to be thermalized completely

    • Results from hadronic cascade models.

  • How is radial flow generated dynamically?

  • Finite radial flow even in pp collisions?

    • (T,vT)~(140MeV,0.2)

    • Is blast wave reliable quantitatively?

  • Consistency?

    • Chi square minimum located a different point for f and W

  • Flow profile? Freezeout hypersurface? Sudden freezeout?


Basic checks necessary conditions to study qgp at rhic

Basic Checks  Necessary Conditions to Study QGP at RHIC

  • Energy density can be well above ec.

    • Thermalized?

  • “Temperature” can be extracted.

    • Why freezeout happens so close to Tc?

  • High pressure can be built up.

    • Completely equilibrated?

Importance of systematic study based on dynamical framework


Dynamics of heavy ion collisions

Dynamics of Heavy Ion Collisions


Dynamics of heavy ion collisions1

Dynamics of Heavy Ion Collisions

Freezeout

“Re-confinement”

Expansion, cooling

Thermalization

First contact

(two bunches of gluons)

Time scale

10fm/c~10-23sec

<<10-4(early universe)

Temperature scale 100MeV~1012K


N coll n part

y

Ncoll & Npart

Thickness function:

x

Gold nucleus:

r0=0.17 fm-3

R=1.12A1/3-0.86A-1/3

d=0.54 fm

Woods-Saxon nuclear density:

# of binary collisions

# of participants

sin = 42mb @200GeV

1-(survival probability)


Centrality

Centrality

Npart and Ncoll as a function of

impact parameter

PHENIX: Correlation btw. BBC and ZDC signals


Toward understanding of quark gluon plasma in relativistic heavy ion collisions

Elliptic Flow


What is elliptic flow

What is Elliptic Flow?

Ollitrault (’92)

How does the system respond to spatial anisotropy?

No secondary interaction

Hydro behavior

y

f

x

INPUT

Spatial Anisotropy

2v2

Interaction among

produced particles

dN/df

dN/df

OUTPUT

Momentum Anisotropy

0

f

2p

0

f

2p


Time evolution of a qgp fluid

Time Evolution of a QGP Fluid

TH&Gyulassy(’06)

QGP

mixed

hadron

Anisotropy of energy density distribution

 Anisotropy of “Momentum” distribution


V 2 from a boltzmann simulation

v2 from a Boltzmann simulation

Zhang et al.(’99)

ideal hydro limit

: Ideal hydro

v2

: strongly

interacting

system

b = 7.5fm

t(fm/c)

generated through secondary collisions

saturated in the early stage

sensitive to cross section (~1/m.f.p.~1/viscosity)

v2 is


Schematic picture of shear viscosity

Schematic Picture of Shear Viscosity

See, e.g. Danielewicz&Gyulassy(’85)

Assuming relativistic particles,

Perfect fluid:

l=1/sr  0

shear viscosity  0

Smearing of flow

Shear flow

Next time step


Basis of the announcement

Basis of the Announcement

STAR(’02)

PHENIX(’03)

“Hydro limit”

response =

(output)/(input)

pT dependence

and mass ordering

Multiplicity dependence

Hydro results: Huovinen, Kolb, Heinz,…

It is found that they reproduce v2(pT) data accidentally.

T.Hirano and M.Gyulassy,Nucl.Phys.A769 (2006)71.


Toward understanding of quark gluon plasma in relativistic heavy ion collisions

Recent Hydro Resultsfrom Our Group


Bottom up approach

Bottom-Up approach

  • The first principle (QuantumChromo Dynamics)

  • Inputs to phenomenology (lattice QCD)

Complexity

Non-linear interactions of gluons

Strong coupling

Dynamical many body system

Color confinement

  • Phenomenology (hydrodynamics)

  • Experimental data

  • @ Relativistic Heavy Ion Collider

    • ~150 papers from 4 collaborations

    • since 2000


Why hydrodynamics

Why Hydrodynamics?

  • Static

  • EoS from Lattice QCD

  • Finite T, m field theory

  • Critical phenomena

  • Chiral property of hadron

Once one accepts local

thermalization ansatz,

life becomes very easy.

Energy-momentum:

Conserved number:

  • Dynamic Phenomena in HIC

  • Expansion, Flow

  • Space-time evolution of

  • thermodynamic variables


Dynamics of heavy ion collisions2

Dynamics of Heavy Ion Collisions

Freezeout

“Re-confinement”

Expansion, cooling

Thermalization

First contact

(two bunches of gluons)

  • Inputs in hydrodynamic simulations:

  • Initial condition

  • Equation of state

  • Decoupling prescription


Centrality dependence of v 2

Centrality Dependence of v2

TH et al. (’06).

  • Discovery of “Large” v2 at RHIC

  • v2 data are comparable with hydro results.

  • Hadronic cascade cannot reproduce data.

  • Note that, in v2 data, there exists eccentricity fluctuation which is not considered in model calculations.

Result from a hadronic cascade (JAM)

(Courtesy of M.Isse)


Pseudorapidity dependence of v 2

TH(’02); TH and K.Tsuda(’02); TH et al. (’06).

Pseudorapidity Dependence of v2

QGP+hadron

  • v2 data are comparable with hydro results again around h=0

  • Not a QGP gas  sQGP

  • Nevertheless, large discrepancy in forward/backward rapidity

  • See next slides

QGP only

h=0

h<0

h>0


Hadron gas instead of hadron fluid

Hadron Gas Instead of Hadron Fluid

T.Hirano and M.Gyulassy,Nucl.Phys.A769 (2006)71.

A QGP fluid surrounded

by hadronic gas

“Reynolds number”

QGP core

Matter proper part:

(shear viscosity)

(entropy density)

big

in Hadron

small

in QGP

QGP: Liquid (hydro picture)

Hadron: Gas (particle picture)


Importance of hadronic corona

Importance of Hadronic “Corona”

  • Boltzmann Eq. for hadrons instead of hydrodynamics

  • Including viscosity through finite mean free path

QGP fluid+hadron gas

QGP+hadron fluids

QGP only

  • Suggesting rapid increase of entropy density

  • Deconfinement makes hydro work at RHIC!?

  •  Signal of QGP!?

T.Hirano et al.,Phys.Lett.B636(2006)299.


Qgp liquid hadron gas picture works well

QGP Liquid + Hadron Gas Picture Works Well

20-30%

  • Centrality dependence is ok

  • Large reduction from pure hydro in small multiplicity events

Mass dependence is o.k.

Note: First result was obtained

by Teaney et al.

T.Hirano et al.,Phys.Lett.B636(2006)299.


Qgp liquid hadron gas picture works well contd

QGP Liquid + Hadron Gas Picture Works Well (contd.)

hybrid model

AMPT

Adopted from S.J.Sanders

(BRAHMS) talk @ QM2006


Toward understanding of quark gluon plasma in relativistic heavy ion collisions

How Fragile/Robustthe Perfect Fluid Discovery is


1 is mass ordering for v 2 p t a signal of the perfect qgp fluid

1. Is mass ordering for v2(pT) a signal of the perfect QGP fluid?

Pion

20-30%

Proton

Mass ordering comes from

rescattering effect. Interplay btw. radial and elliptic flows

Not a direct sign of the perfect QGP fluid

Mass dependence is o.k. from

hydro+cascade.


Why they shift oppositely

Why they shift oppositely?

pions

protons

v2(pT)

v2

<pT>

pT

v2 for protons can be negative

even in positive elliptic flow

must decrease with proper time

P.Huovinen et al.,PLB503,58(01)

TH and M.Gyulassy, NPA769,71(06)


Violation of mass ordering

Violation of Mass Ordering

Early decoupling from the system for phi mesons

Mass ordering is generated during hadronic evolution.

TH et al., arXiv:0710.5795[nucl-th].


2 is viscosity really small in qgp

2. Is viscosity really small in QGP?

  • 1+1D Bjorken flow Bjorken(’83)

  • Baym(’84)Hosoya,Kajantie(’85)Danielewicz,Gyulassy(’85)Gavin(’85)Akase et al.(’89)Kouno et al.(’90)…

(Ideal)

(Viscous)

h: shear viscosity (MeV/fm2), s : entropy density (1/fm3)

h/s is a good dimensionless measure

(in the natural unit) to see viscous effects.

Shear viscosity is small in comparison with entropy density!


A probable scenario

TH and Gyulassy (’06)

A Probable Scenario

h: shear viscosity, s : entropy density

Kovtun,Son,Starinets(’05)

  • Absolute value of viscosity

  • Its ratio to entropy density

!

Rapid increase of entropy density can

make hydro work at RHIC.

Deconfinement Signal?!


Digression

Digression

[Pa] = [N/m2]

(Dynamical) Viscosity h:

~1.0x10-3 [Pa s] (Water20℃)

~1.8x10-5 [Pa s] (Air 20℃)

Kinetic Viscosity n=h/r:

~1.0x10-6 [m2/s] (Water20℃)

~1.5x10-5 [m2/s] (Air20℃)

hwater > hair BUT nwater < nair

Non-relativistic Navier-Stokes eq. (a simple form)

Neglecting external force and assuming incompressibility.


3 is h s enough

3. Is h/s enough?

  • Reynolds number

Iso, Mori, Namiki (’59)

R>>1

Perfect fluid

  • (1+1)D Bjorken solution

  • Need to solve viscous fluid dynamics in (3+1)D

  • Cool! But, tough!

  • Causality problem


4 boltzmann at work

4. Boltzmann at work?

Molnar&Gyulassy(’00)

Molnar&Huovinen(’04)

25-30%

reduction

gluonic

fluid

s ~ 15 * spert !

Caveat 1: Where is the “dilute” approximation in Boltzmann

simulation? Is l~0.1fm o.k. for the Boltzmann description?

Caveat 2: Differential v2 is tricky. dv2/dpT~v2/<pT>.

Difference of v2 is amplified by the difference of <pT>.

Caveat 3: Hadronization/Freezeout are different.


5 does v 2 p t really tell us smallness of h s in the qgp phase

5. Does v2(pT) really tell us smallness of h/s in the QGP phase?

D.Teaney(’03)

  • Not a result from dynamical calculation, but a “fitting” to data.

  • No QGP in the model

  • t0 is not a initial time, but a freeze-out time.

  • Gs/t0 is not equal to h/s, but to 3h/4sT0t0 (in 1+1D).

  • Being smaller T0 from pT dist., t0 should be larger (~10fm/c).


6 is there model dependence in hydro calculations

6. Is there model dependence in hydro calculations?

Novel initial conditions

from Color Glass Condensate

lead to large eccentricity.

Hirano and Nara(’04), Hirano et al.(’06)

Kuhlman et al.(’06), Drescher et al.(’06)

Need viscosity and/or

softer EoS in the QGP!


Summary

Summary

  • Agreement btw. hydro and data comes from one particular modeling. (Glauber + ideal QGP fluid + hadron gas)

  • IMO, still controversial for discovery of perfect fluid QGP.

  • Check model dependences to obtain robust conclusion (and toward comprehensive understanding of the QGP from exp. data).


Heavy ion caf

Heavy Ion Café

http://tkynt2.phys.s.u-tokyo.ac.jp/~hirano/hic/index.html


  • Login